Plastic mats or runners are commonly employed to provide cushioning and shock-absorbing covering surfaces for objects or people. In particular, vinyl chloride plastic mats and runners composed of a vinyl chloride foam or solid layers, or combinations thereof, are often used as flexible surface coverings. Such plastic mats are often manufactured employing one or more reinforcing layers in order to impart dimensional stability to the plastic mat, such as, for example, the employment of fibrous sheet materials, such as nylon, polyester or glass fiber scrim tissue sheet material embedded within the thermoplastic layer which makes up the plastic mat (see U.S. Pat. No. 4,710,415, issued Dec. 1, 1987).
Plastic mats or runners are often employed in areas containing sensitive electronic equipment, such as in clean rooms. Such mats are often treated or manufactured to have static-reducIng properties in order to reduce static charges which build up on persons or objects. The static-reducing surface covering material is electrically conductive and is antistatic in the sense that it reduces static and prevents the generation of a substantially instantaneous spark discharge, and yet is sufficiently electrically resistant so as not to be wholly electrically conductive and to control the discharge of accumulated static.
One electrically conductive web for discharging static electricity is described in U.S. Pat. No. 4,208,696. The electrically conductive web material for discharging static electricity includes a semiconductive, thermoplastic polymeric layer in contact with a foraminous layer, such as of foam or scrim, coated with a carbon-loaded, resinous material to impart a resistivity of between 10.sup.3 ohms and 10.sup.7 ohms. U.S. Pat. No. 4,525,398 discloses a thin layer of metallic foil bonded to a hard layer of plastic material by way of an electrically conductive adhesive material and a layer of backing material secured to the metallic foil. U.S. Pat. No. 4,363,071 relates to a static dissipative mat with a conductive inner layer of low surface resistance. The inner conductive layer comprises a thin film containing an electrically conductive ingredient, such as carbon black having a low surface resistivity. U.S. Pat. No. 4,472,471 concerns a hard, transparent, chair mat having a carbon-loaded, electrically conductive printing in grid disposed on the transparent plastic, while U.S. Pat. No. 4,590,120 also relates to a transparent, static-reducing chair mat containing a plurality of thin, conductive, invisible fibers forming a static-charge-draining, conductive layer within the mat, such as stainless steel fibers, between the upper and lower layers.
It is therefore desirable to provide a static-reducing, plastic surface covering material which effectively controls static without excessive electric conductivity, is dimensionally stable and resists delamination and which surface covering is easily manufactured at low cost.